Microfeature workpiece processing apparatus and methods for controlling deposition of materials on microfeature workpieces

ABSTRACT

The present disclosure provides methods and apparatus useful in depositing materials on batches of microfeature workpieces. One implementation provides a method in which a quantity of a first precursor gas is introduced to an enclosure at a first enclosure pressure. The pressure within the enclosure is reduced to a second enclosure pressure while introducing a purge gas at a first flow rate. The second enclosure pressure may approach or be equal to a steady-state base pressure of the processing system at the first flow rate. After reducing the pressure, the purge gas flow may be increased to a second flow rate and the enclosure pressure may be increased to a third enclosure pressure. Thereafter, a flow of a second precursor gas may be introduced with a pressure within the enclosure at a fourth enclosure pressure; the third enclosure pressure is desirably within about 10 percent of the fourth enclosure pressure.

TECHNICAL FIELD

The present invention is related to equipment and methods for processingmicrofeature workpieces, e.g., semiconductor wafers. Aspects of theinvention have particular utility in connection with batch deposition ofmaterials on microfeature workpieces by atomic layer deposition.

BACKGROUND

Thin film deposition techniques are widely used in the manufacturing ofmicrofeatures to form a coating on a workpiece that closely conforms tothe surface topography. In the context of microelectronic components,for example, the size of the individual components in the devices on awafer is constantly decreasing, and the number of layers in the devicesis increasing. As a result, the density of components and the aspectratios of depressions (e.g., the ratio of the depth to the size of theopening) are increasing. The size of such wafers is also increasing toprovide more real estate for forming more dies (i.e., chips) on a singlewafer. Many fabricators are currently transitioning from 200 mm to 300mm workpieces, and even larger workpieces will likely be used in thefuture. Thin film deposition techniques accordingly strive to producehighly uniform conformal layers that cover the sidewalls, bottoms, andcorners in deep depressions that have very small openings.

One widely used thin film deposition technique is chemical vapordeposition (CVD). In a CVD system, one or more precursors that arecapable of reacting to form a solid thin film are mixed in a gas orvapor state, and then the precursor mixture is presented to the surfaceof the workpiece. The surface of the workpiece catalyzes the reactionbetween the precursors to form a solid thin film at the workpiecesurface. A common way to catalyze the reaction at the surface of theworkpiece is to heat the workpiece to a temperature that causes thereaction.

Although CVD techniques are useful in many applications, they also haveseveral drawbacks. For example, if the precursors are not highlyreactive, then a high workpiece temperature is needed to achieve areasonable deposition rate. Such high temperatures are not typicallydesirable because heating the workpiece can be detrimental to thestructures and other materials already formed on the workpiece.Implanted or doped materials, for example, can migrate within siliconworkpieces at higher temperatures. On the other hand, if more reactiveprecursors are used so that the workpiece temperature can be lower, thenreactions may occur prematurely in the gas phase before reaching theintended surface of the workpiece. This is undesirable because the filmquality and uniformity may suffer, and also because it limits the typesof precursors that can be used.

Atomic layer deposition (ALD) is another thin film deposition technique.FIGS. 1A and 1B schematically illustrate the basic operation of ALDprocesses. Referring to FIG. 1A, a layer of gas molecules A coats thesurface of a workpiece W. The layer of A molecules is formed by exposingthe workpiece W to a precursor gas containing A molecules, and thenpurging the chamber with a purge gas to remove excess A molecules. Thisprocess can form a monolayer of A molecules on the surface of theworkpiece W because the A molecules at the surface are held in placeduring the purge cycle by physical adsorption forces at moderatetemperatures or chemisorption forces at higher temperatures. The layerof A molecules is then exposed to another precursor gas containing Bmolecules. The A molecules react with the B molecules to form anextremely thin layer of solid material C on the workpiece W. The chamberis then purged again with a purge gas to remove excess B molecules.

FIG. 2 illustrates the stages of one cycle for forming a thin solidlayer using ALD techniques. A typical cycle includes (a) exposing theworkpiece to the first precursor A, (b) purging excess A molecules, (c)exposing the workpiece to the second precursor B, and then (d) purgingexcess B molecules. The purge process typically comprises introducing apurge gas, which is substantially non-reactive with either precursor,and exhausting the purge gas and excess precursor from the reactionchamber in a pumping step. In actual processing, several cycles arerepeated to build a thin film on a workpiece having the desiredthickness. For example, each cycle may form a layer having a thicknessof approximately 0.5-1.0Å, and thus it takes approximately 60-120 cyclesto form a solid layer having a thickness of approximately 60Å.

One drawback of ALD processing is that it has a relatively lowthroughput compared to CVD techniques. For example, ALD processingtypically takes several seconds to perform each A-purge-B-purge cycle.This results in a total process time of several minutes to form a singlethin layer of only 60Å. In contrast to ALD processing, CVD techniquesonly require about one minute to form a 60Å thick layer. In single-waferprocessing chambers, ALD processes can be 500%-2000% longer thancorresponding single-wafer CVD processes. The low throughput of existingsingle-wafer ALD techniques limits the utility of the technology in itscurrent state because ALD may be a bottleneck in the overallmanufacturing process.

One promising solution to increase the throughput of ALD processing isprocessing a plurality of wafers (e.g., 20-250) simultaneously in abatch process. As suggested in International Publication No. WO02/095807, the entirety of which is incorporated herein by reference,such batch processes typically stack the plurality of wafers in a waferholder that is positioned in an enclosure of a processing system. Toincrease the number of wafers that can be treated at one time andconcomitantly increase the throughput of the system, the wafers aretypically held in a relatively close spaced-apart relationship.Unfortunately, this close spacing between adjacent wafers hinders theflow of gas adjacent the surface of the wafer, particularly adjacent thecenter of each wafer.

In conventional single-wafer ALD systems, a gas “showerhead” will bespaced in relatively close, parallel proximity with substantially theentirety of the wafer surface. This facilitates thorough, effectivepurging of the excess precursors A and B. In a batch ALD system,however, gas is typically introduced to flow longitudinally alongsidethe wafer holder. As a consequence, gas exchange between the waferstakes place, in large part, by gas diffusion rather than a significantflow rate of gas across the wafer surface. To enhance the removal ofexcess precursor between the wafers, conventional batch ALD processingtypically involves introducing a significant quantity of a purge gas todilute the remaining precursor, then drawing a vacuum on the enclosureto remove the diluted gas. Unfortunately, this addition of excess purgegas and subsequent pump-down can take a relatively long period of time,further reducing the throughput of the batch ALD processing system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic cross-sectional views of stages in ALDprocessing in accordance with the prior art.

FIG. 2 is a graph illustrating a cycle for forming a layer using ALDtechniques in accordance with the prior art.

FIG. 3 is a schematic cross-sectional view of a microfeature workpieceprocessing system in accordance with an embodiment of the invention.

FIG. 4 is a schematic flow diagram illustrating aspects of a method inaccordance with one embodiment of the invention.

FIG. 5 is a flow diagram schematically illustrating aspects of oneembodiment of the pump/purge steps in FIG. 4.

FIG. 6 is a graph schematically illustrating gas pressures and flowrates in accordance with one particular embodiment of the invention.

FIG. 7 is a graph schematically illustrating partial pressure of aprecursor gas during various pump and/or purge processes.

DETAILED DESCRIPTION

A. Overview

Various embodiments of the present invention provide microfeatureworkpiece holders, systems including processing chambers, and methodsfor depositing materials onto microfeature workpieces. Many specificdetails of the invention are described below with reference to reactorsfor depositing materials onto microfeature workpieces. The term“microfeature workpiece” is used throughout to include substrates uponwhich and/or in which microelectronic devices, micromechanical devices,data storage elements, read/write components, and other devices arefabricated. For example, microfeature workpieces can be semiconductorwafers such as silicon or gallium arsenide wafers, glass substrates,insulative substrates, and many other types of materials. Themicrofeature workpieces typically have submicron features withdimensions of 0.05 microns or greater. Furthermore, the term “gas” isused throughout to include any form of matter that has no fixed shapeand will conform in volume to the space available, which specificallyincludes vapors (i.e., a gas having a temperature less than the criticaltemperature so that it may be liquefied or solidified by compression ata constant temperature). Several embodiments in accordance with theinvention are set forth in FIGS. 3-6 and the following text to provide athorough understanding of particular embodiments of the invention. Aperson skilled in the art will understand, however, that the inventionmay have additional embodiments, or that the invention may be practicedwithout several of the details of the embodiments shown in FIGS. 3-6.

One embodiment of the invention provides a method of depositing amaterial on a microfeature workpiece. In accordance with this method, aplurality of microfeature workpieces are positioned in a spacedrelationship within an enclosure. A flow of a first precursor gas isintroduced to the enclosure at a first enclosure pressure. The flow ofthe first precursor is terminated and pressure within the enclosure isreduced to a second enclosure pressure while introducing a flow of apurge gas at a first flow rate. The processing system has a basepressure at the first flow rate. A difference between the secondenclosure pressure and the first enclosure pressure is at least 90percent of the difference between the base pressure and the firstenclosure pressure. After reducing the pressure within the enclosure tothe second enclosure pressure, the flow rate of the purge gas isincreased to a second flow rate and the pressure within the enclosure isincreased to a third enclosure pressure. After increasing the pressurewithin the enclosure to the third enclosure pressure, a flow of a secondprecursor gas is introduced to the enclosure at a fourth enclosurepressure. The third and fourth enclosure pressures may be substantiallythe same, with any difference between the third and fourth enclosurepressures being about 0-10 percent of the fourth enclosure pressure.

A method in accordance with another embodiment of the invention may alsobe used to deposit a material on a microfeature workpiece. In thismethod, a plurality of microfeature workpieces, each of which has asurface, is positioned within an enclosure. The surfaces of themicrofeature workpieces are exposed to a first precursor gas at a firstenclosure pressure to allow at least a monolayer of the first precursorgas to be adsorbed on the surfaces of the microfeature workpieces.Pressure within the enclosure is reduced to a second, lower enclosurepressure via a pump-down process. The pump-down process compriseswithdrawing gas from the enclosure, e.g., with a vacuum, whileintroducing a purge gas at a first flow rate of no greater than about250 sccm for a first period of time. This pump-down process reduces thepartial pressure of the first precursor gas within the enclosure. Afterthe pump-down process, the enclosure is purged in a purge process thatincludes introducing the purge gas at a second flow rate of at leastabout 1000 sccm for a second period of time and allowing the enclosurepressure to increase to a third enclosure pressure that is greater thanthe second enclosure pressure. After the purge process, the surfaces ofthe microfeature workpieces may be exposed to a second precursor gas ata fourth enclosure pressure. The third and fourth enclosure pressuresmay be substantially the same, with any difference between the third andfourth enclosure pressures desirably being about 0-10 percent of thefourth enclosure pressure.

Another embodiment of the invention provides a microfeature workpieceprocessing system that includes an enclosure, a gas supply, a vacuum,and a programmable controller. The enclosure is adapted to receive aplurality of microfeature workpieces for simultaneous treatment. The gassupply is adapted to selectively deliver a first gaseous precursor, asecond gaseous precursor, and a purge gas to the enclosure. Theprogrammable controller is operatively coupled to the gas supply and thevacuum, and the controller may be programmed to carry out one of theaforementioned methods or methods in accordance with other aspects ofthe invention.

For ease of understanding, the following discussion is subdivided intotwo areas of emphasis. The first section discusses microfeatureworkpiece processing systems in accordance with selected embodiments ofthe invention. The second section outlines methods in accordance withother aspects of the invention.

B. Microfeature Workpiece Processing Systems

FIG. 3 schematically illustrates a reactor 10 in accordance with oneembodiment of the invention. This reactor 10 includes a processingenclosure 20 coupled to a gas supply 30 and a vacuum 40. The processingenclosure 20 generally includes an outer wall 22 and an annular liner24. A platform 60 seals against the outer wall or some other part of theprocessing enclosure 20 to define a deposition chamber 25. The liner 24functionally divides the deposition chamber 25 into a main chamber 28and an annular exhaust 26.

One or more microfeature workpieces W, e.g., semiconductor wafers, maybe positioned in the deposition chamber 25 for processing. In theillustrated embodiment, a plurality of microfeature workpieces W areheld in the processing enclosure 20 in a workpiece holder 70. It shouldbe understood that FIG. 3 is merely schematic in nature and any number(e.g., 20-250) of workpieces W may be held in the workpiece holder 70for simultaneous batch processing.

The reactor 10 also includes at least one heat source to heat theworkpieces W and maintain them at the desired temperature. The heatsource in FIG. 3 is typified as a radiant heater 50 comprising a seriesof radiant heat panels 50 a and 50 b arranged about a circumference ofthe enclosure 20 to evenly heat the workpieces W. In one embodiment,these heat panels 50 a-b comprise quartz-halogen lamps or other types ofradiative heat sources. In other embodiments, other types of heatsources may be employed. The heater 50 may also include a power supply52 that is coupled to the first heat panel 50 a by a first power line 54a and to the second heat panel 50 b by a second power line 54 b.

Gas is introduced from the gas supply 30 to the deposition chamber 25 bya gas line 32 and an inlet 36. The inlet 36 directs a flow of gas intothe main chamber 28 of the deposition chamber 25. Under influence of thevacuum 40, gas introduced via the gas inlet 36 will flow through themain chamber 28, outwardly into the annular exhaust 26, and out of thedeposition chamber 25. A valve assembly 34 in the gas line 32 may beoperated by a controller 90 to selectively deliver gases to thedeposition chamber 25 during the deposition phase. In one embodiment,the controller 90 comprises a computer having a programmable processorprogrammed to control operation of the reactor 10 to deposit material onthe workpieces W in accordance with one or more of the methods outlinedbelow. The controller 90 may be coupled to the vacuum 40 to control itsoperation. The controller 90 may also be operatively connected to theheater 50, e.g., via the power supply 52, to control the temperature ofthe workpieces W. [0026] Some aspects of the gas supply 30 will dependon the nature of the deposition process to be carried out in the reactor10. In one embodiment, the reactor 10 is adapted to carry out an ALDprocess employing multiple precursors. The gas supply 30 in suchembodiments can include a plurality of separate gas sources 31 a-c, andthe valve assembly 34 may have a plurality of valves. For example, thegas supply 30 may include one or more gaseous precursors capable ofreacting to deposit titanium nitride. In one such implementation, thefirst gas source 31 a is adapted to deliver TiCl₄, the second gas source31 b is adapted to deliver NH₃, and the third gas source 31c is adaptedto deliver a flow of a purge gas, e.g., nitrogen.

C. Methods of Depositing Materials on Microfeature Workpieces

As noted above, other embodiments of the invention provide methods ofprocessing microfeature workpieces. In the following discussion,reference is made to the particular microfeature workpiece processingsystem 10 shown in FIG. 3. It should be understood, though, thatreference to this particular processing system is solely for purposes ofillustration and that the methods outlined below are not limited to anyparticular processing system shown in the drawings or discussed indetail above.

FIGS. 4 and 5 schematically illustrate aspects of a method of depositinga material on surfaces of a batch of microfeature workpieces inaccordance with one embodiment of the invention; FIG. 4 provides anoverview, whereas FIG. 5 provides details of certain aspects of FIG. 4.Turning first to FIG. 4, the workpiece manufacturing process 100 may beinitiated by positioning the workpieces W in the enclosure 20 of an ALDreactor 10 or other processing system (process 105). In process 110, theambient atmosphere that entered the main chamber 25 of the enclosure 20may be withdrawn, e.g., by means of the vacuum 40 and a flow of an inertpurge gas (e.g., nitrogen from the third gas source 31 c of the gassupply 30). If necessary, the workpieces W may also be heated to thedesired process temperature by the heaters 50.

With the majority of any deleterious gases removed from the depositionchamber 25, a flow of the first precursor gas may be initiated inprocess 115 and terminated in process 120. This will deliver a pulse ofthe first precursor gas into the deposition chamber 25, exposing asurface of each of the workpieces W in the deposition chamber 25 to thefirst precursor. The first precursor may be at least chemisorbed on theworkpiece W. Theoretically, such chemisorption will form a monolayerthat is uniformly one molecule thick on the entire surface of theworkpiece W. Such a monolayer may be referred to as a saturatedmonolayer. As a practical matter, in some circumstances some minorportions of the workpiece surface may not chemisorb a molecule of theprecursor. Nevertheless, such imperfect monolayers are still referred toherein as monolayers. In many applications, a substantially saturatedmonolayer may be suitable. A substantially saturated monolayer is amonolayer that will yield a deposited layer exhibiting the requisitequality and/or performance parameters.

As is known in the art, an excess of the first precursor gas istypically delivered to the processing enclosure 20. This excess firstprecursor gas is desirably removed from the vicinity of the workpiecesurface prior to introduction of the second precursor gas. Inadequateremoval of the first precursor gas prior to introduction of the secondprecursor gas may result in a gaseous phase reaction between theprecursors that yields a material that is less conformal to thetopography of the workpiece surface or otherwise adversely affects thequality of the deposited material. Consequently, in the manufacturingprocess 100 of FIG. 4, a pump/purge process 200 (detailed below) iscarried out before introducing the second precursor gas to the enclosure20. After the pump/purge process 200, a flow of the second precursor gasmay be initiated in process 130 to deliver a pulse of the secondprecursor gas to the enclosure 20. This second precursor may chemisorbon the first monolayer of the first precursor and/or react with themonolayer to form a reaction product. This reaction product is typicallyone or no more than a few molecules thick, yielding a very thin, highlyconformal nanolayer reaction product. After a suitable exposure to thesecond gaseous precursor, the flow of the second precursor gas may beterminated in process 135 and a pump/purge process 200 may again beperformed.

This series of first precursor—pump/purge—second precursor—pump/purgeprocesses may be considered one ALD cycle adapted to deposit a singlenanolayer of material. As noted above, the ALD process may need to berepeated a number of times to deposit a layer of material having anappropriate thickness. The manufacturing process 100 of FIG. 4 may thusinclude a decision process 140 that decides whether the layer depositedon the microfeature workpieces W is thick enough. In many circumstances,this decision will comprise determining whether a fixed number ofdeposition cycles, which has been empirically determined to deposit anadequate thickness, has been performed. If a sufficient thickness hasnot been deposited, the manufacturing process 100 may return to process115 to deposit another thickness of the reaction product. If thethickness is determined in process 140 to be sufficient, though, theworkpieces W may be removed from the enclosure 20 in process 145.

FIG. 5 schematically illustrates the pump/purge process 200 of FIG. 4 ingreater detail. This pump/purge process 200 generally includes a pumpprocess 210 and a purge process 220. The pump process 210 may includeintroducing a flow of purge gas at a first flow rate (process 212) andwithdrawing gas from the enclosure 20 until a target pressure is reached(process 214). If the vacuum system 40 of the reactor 10 is sufficientlyrobust, it may be possible to omit the flow of purge gas in process 212and instead merely withdraw gas from the enclosure 20 with the vacuum 40in process 214. This will reduce the pressure within the enclosure 20more rapidly, reducing the time necessary for the pump process 210. Formany commercial reactors 10, however, it may be advantageous to continuea flow of purge gas at a relatively low flow rate to reduce the chancesof any backflow from or cross-contamination in the vacuum 40.

The first flow rate suitable in process 212 will depend in part on thedesign of the reactor 10, including its size and geometry, and theprecursor being removed. In many commercial applications, though, afirst flow rate of no greater than about 250 standard cubic centimetersper minute (sccm) will suffice. A flow rate of 0-250 sccm will beappropriate for most applications, but a flow rate of 50-250 sccm, e.g.,50-100 sccm, is preferred for select embodiments. The particularembodiment illustrated in FIG. 5 shows the introduction of the purge gasin process 212 before withdrawing gas from the enclosure in process 214.In other embodiments, the order of processes 212 and 214 may be reversedor processes 212 and 214 may start and end simultaneously.

After the pump process 210, the pump/purge process 200 of FIG. 5continues with the purge process 220. This purge process 220 includesincreasing the flow of purge gas to a second flow rate in process 222and increasing pressure in the enclosure 20 to a process pressure 224that is higher than the target pressure in process 214. In oneembodiment, the second flow rate in process 222 is at least about fourtimes the first flow rate (process 212), though this multiple may besignificantly higher. It is anticipated that a second flow rate of atleast 1000 sccm will be best in most circumstances. In embodimentsemploying commercial-scale batch ALD reactors 10, a second flow rate ofno less than 2000 sccm may be advantageous.

FIGS. 4 and 5 provide an overview of the manufacturing process 100. FIG.6 provides a schematic illustration of one particular implementation ofthe manufacturing process 100 that highlights some of the aspects andadvantages of select embodiments of the invention. The upper graph ofFIG. 6 illustrates the pressure in the processing enclosure 20 over thecourse of part of the manufacturing process 100. The bottom graph ofFIG. 6 is a schematic plot of the flow rate of a purge gas, a firstprecursor gas, and a second precursor gas as a function of time. Thetime scale in both graphs of FIG. 6 is the same.

The timeline of FIG. 6 starts with the initiation of the flow of thefirst precursor gas in process 115 of FIG. 4. (Like reference numbersare used in FIGS. 4-6 to indicate like processes.) The flow of the firstprecursor gas will continue until it is terminated in process 120,whereupon the pump/purge process 200 may begin. As shown in the topgraph of FIG. 6, the pressure in the main chamber 28 of the enclosure 20may remain substantially constant at a selected process pressure Pduring the first precursor gas pulse. The process pressure P will varydepending on the nature of the deposition process being carried out,e.g., the nature of the first and second precursor gases, thetemperature of the workpieces W, the volume and dimensions of theenclosure 20, and other operating parameters.

As noted above, the pump/purge process 200 includes a pump-down process210 and a purge process 220. In the pump-down process 210, the flow ofpurge gas may be relatively low, e.g., 50-100 sccm. With the vacuum 40activated, the pressure in the main chamber 28 of the enclosure willdrop fairly rapidly, as suggested by curve X in the upper graph of FIG.6. For any particular reactor 10 design and first flow rate during thepump-down process 210, the main chamber 28 of the enclosure 20 will havea substantially steady-state lower pressure identified in FIG. 6 as basepressure B.

In the purge process 220, the flow rate of the purge gas is increasedand the pressure within the main chamber 28 of the enclosure 20 isallowed to increase (curve Y). In one particular embodiment, theenclosure pressure at the end of the purge process 220 is similar to theprocess pressure P at which the workpieces W will be exposed to thesecond precursor gas. In one particular embodiment, a difference betweenthe enclosure pressure at the end of the purge process 220 and thedesired process pressure P at which the workpieces W will be exposed tothe second precursor gas is about 0-10% of the process pressure P. Inthe particular scenario illustrated in the top graph of FIG. 6, thepressure in the enclosure may slightly exceed the process pressure P,but be brought back down to the process pressure P by the end of thepump/purge process 200. If the flow of the second precursor gas wereinitiated in process 130 when the enclosure pressure is at or close tothe base pressure B, the controller 90 is likely to overshoot thedesired process pressure P before stabilizing the enclosure pressure.Overshooting the process pressure P with the flow of the secondprecursor can introduce undesirable variations in the exposure of theworkpieces W to the second precursor gas from one cycle to the next. Byincreasing the enclosure pressure during the purge process 220, thelikelihood of overshooting the process pressure P with the secondprecursor gas can be materially reduced. In the particular scenarioillustrated in FIG. 6, the enclosure pressure may overshoot the processpressure P during the purge process 220, but the enclosure pressure maybe substantially stabilized at the process pressure P before the flow ofthe second precursor gas is initiated in process 130. This can enhanceuniformity of the process from one cycle to the next.

One objective of the pump/purge process 200 is to reduce theconcentration of any excess, nonadsorbed precursor gas in at least themain chamber 28 of the enclosure 20 to an acceptable level. The firstprecursor—pump/purge—second precursor—pump/purge cycle typically must berepeated numerous times to deposit a suitable thickness of material onthe surfaces of the workpieces W. Reducing the time of the pump/purgeprocess 200, therefore, can materially decrease the time needed to reachthe suitable material thickness.

FIG. 7 is a schematic graph comparing the expected concentration of aprecursor, expressed as a partial pressure of the precursor in theenclosure, during a purge process 220 only, during a pump-down process210 only, and during a pump/purge process 200 in accordance withembodiments of the invention. In this graph, the process pressure P atwhich the pump/purge process 200 is initiated is arbitrarily set at 1(i.e., 0 on the log scale of FIG. 7).

If the pump-down process 210 were omitted and the purge process 220alone were relied on to reduce concentration of the precursor, one wouldexpect to see the log of the partial pressure of the precursor decreaseat a fairly constant rate over time. This is represented in FIG. 7 bydashed curve 320 a, which is generally linear and has a relativelyconstant first slope S₁. The slope S₁ will vary with a number offactors, including the geometry of the enclosure 20, the relativespacing of the workpieces W, and the rate at which the vacuum withdrawsgas from the enclosure. All other factors being equal, though, the slopeS₁ generally will increase (i.e., the partial pressure will drop morequickly) with increasing flow rates of purge gas into the enclosure. Itshould be recognized that curve 320 a is stylized and the partialpressure of the precursor may deviate noticeably from this relativelystraight line, particularly at higher purge gas flow rates or highervacuum extraction rates.

If the purge process 220 were omitted and the pump-down process alonewere employed, one would expect to see a marked drop-off in the partialpressure of the precursor in a first phase 310, as illustrated in thesolid curve of FIG. 7. Once the base pressure B (FIG. 6) is reached,though, further extraction of precursor from the main chamber 28 of theenclosure 20 is limited largely by the rate at which the precursordiffuses out of the spaces between adjacent workpieces W. Hence, onewould expect to see the log of the partial pressure of the precursordecrease at a fairly constant terminal rate during a second phase 312,yielding a generally linear curve having a second slope S₂. This secondslope S₂ is expected to be less than the first slope S₁ of curve 320 a.One advantage of the pump-down process 210 is that the partial pressureof the precursor drops off rapidly in the first phase 310to quicklyreduce the partial pressure below a level that promotes furtheradsorption. This facilitates more precise control over the time theworkpieces W are exposed to material concentrations of the precursor.

The pump/purge process 200 illustrated in FIGS. 4-6 is expected toachieve benefits of both the pump-down process 210 and the purge process220, yet reduce the total time needed to reduce the concentration ofprecursor in the enclosure to an acceptable level before introducing thenext precursor. In the particular example shown in FIG. 7, the pump-downprocess 210 continues until the enclosure pressure reaches the basepressure B, taking advantage of the rapid decrease in partial pressureof the precursor in the first phase 310 of the pump-down. Rather thancontinuing the second phase 312 of the pump-down process 210, though,the purge process 220 is initiated promptly after reaching the basepressure B. Curve 320 b, which illustrates the partial pressure ofprecursor during this purge process 220, may be a relatively straightline having a slope S₃ that is greater than the slope S₂ of the partialpressure curve in the second phase 312 of the pump-down process 210. Itis anticipated that the slopes S₁ and S₃ of curves 320 a and 320 b,respectively, will be similar and may be substantially the same. Asillustrated in FIG. 7, the increased slope S₃ of curve 320 b compared toslope S₂ during the second pump-down phase 312 will result in a timesavings Δt in achieving the same partial pressure of the precursor. As aconsequence, the pump/purge process 200 will allow the concentration ofprecursor in the main chamber 28 of the enclosure 20 to be reduced tothe same level in a shorter period of time than either the pump-downprocess 210 alone (the solid curve in FIG. 7) or the purge process 220alone (curve 320 a), increasing throughput of the reactor 10.

In the particular embodiment shown in FIG. 7, the purge process 220 isinitiated promptly upon reaching the base pressure B. In otherembodiments, the pump-down process 210 is allowed to continue for alimited time (e.g., 3 seconds or less) thereafter. Because the slope S₂of the partial pressure curve in the second phase 312 of the pump-down210 is less than the slope S₃ of curve 320 b, though, delayinginitiation of the purge process 220 will reduce the time savings Δt. Inother embodiments, the time purge process 220 is initiated before thebase pressure B is reached. In the particular embodiment illustrated inFIG. 6, for example, the purge process 220 starts while the enclosurepressure is slightly higher than the base pressure B achievable in asteady state second phase 312 of the pump-down process 210. In someembodiments of the invention, the purge process 220 is initiated whenthe difference between the enclosure pressure and the process pressure Pis at least 90% of the difference between the base pressure B and theprocess pressure P. In one particular embodiment, the purge process 220is initiated when the difference between the enclosure pressure and theprocess pressure P is at least 90% of the difference between the basepressure B and the process pressure P, but no later than reaching thebase pressure. This will achieve the rapid initial drop-off in partialpressure of the precursor, but initiate the purge process 220 before theless productive second phase 312 of the pump-down process 210.

The diffusion rate of any given gas will vary with pressure, with thediffusion rate increasing as pressure is reduced. Different gasesdiffuse at different rates, though. For example, the diffusion rate Dfor TiCl₄ in nitrogen is expected to be on the order of 0.032 m²/s at anenclosure pressure of about 1 torr, but this diffusion rate willincrease to about 0.80 m²/s at about 0.04 torr. In contrast, NH₃, whichmay be used as a second precursor with TiCl₄ to deposit TiN, has adiffusion rate D in nitrogen of about 0.088 m²/s at about 1 torr, whichclimbs to about 2.2 m²/s at about 0.04 torr. NH₃, therefore, shoulddiffuse out of the spaces between the workpieces W more readily thanTiCl₄.

The curves 310, 312, 320 a, and 320 b in FIG. 7 are expected to followthe same general relationship for most precursor gases, but the preciseshapes of the curves (e.g., the slopes S₁₋₃) will vary from one gas toanother. If the pump-down process 210 continues for a fixed time in allpump/purge processes 200 in the manufacturing process 100 of FIG. 4,this time may be selected so the enclosure pressure is reduced by atleast 90% of the difference between the base pressure B and the processpressure P for both precursor gases. This may dictate that the enclosurepressure at the end of the pump-down process 210 will vary from onepump/purge process 200 to the next. In another embodiment, theparameters of the pump/purge process 200 may be varied depending on thediffusion characteristics of the precursor gas being purged. This willallow each pump/purge process 200 to be optimized, further enhancingthroughput of the reactor 10 without compromising product quality.

The above-detailed embodiments of the invention are not intended to beexhaustive or to limit the invention to the precise form disclosedabove. Specific embodiments of, and examples for, the invention aredescribed above for illustrative purposes, but those skilled in therelevant art will recognize that various equivalent modifications arepossible within the scope of the invention. For example, whereas stepsare presented in a given order, alternative embodiments may performsteps in a different order. The various embodiments described herein canbe combined to provide further embodiments.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense as opposed to anexclusive or exhaustive sense, i.e., in a sense of “including, but notlimited to.” Use of the word “or” in the claims in reference to a listof items is intended to cover a) any of the items in the list, b) all ofthe items in the list, and c) any combination of the items in the list.

In general, the terms used in the following claims should not beconstrued to limit the invention to the specific embodiments disclosedin the specification unless the above-detailed description explicitlydefines such terms. While certain aspects of the invention are presentedbelow in certain claim forms, the inventors contemplate various aspectsof the invention in any number of claim forms. Accordingly, theinventors reserve the right to add additional claims after filing theapplication to pursue such additional claim forms for other aspects ofthe invention.

1. A method of depositing a material on a plurality of microfeatureworkpieces held in a spaced relationship within an enclosure of aprocessing system, the enclosure including a first precursor gas andhaving a first enclosure pressure, the method comprising: reducingpressure within the enclosure to a second enclosure pressure whileintroducing a flow of a purge gas into the enclosure at a first flowrate, the second enclosure pressure being less than the first enclosurepressure, the processing system having a base pressure at the first flowrate, and a difference between the second enclosure pressure and thefirst enclosure pressure being at least 90% of the difference betweenthe base pressure and the first enclosure pressure; and after reducingthe pressure within the enclosure to the second enclosure pressure,increasing flow rate of the purge gas to a second flow rate andincreasing the pressure within the enclosure to a third enclosurepressure, the second flow rate being greater than the first flow rateand the third enclosure pressure being greater than the second enclosurepressure.
 2. The method of claim 1 wherein the first flow rate is nogreater than about 250 sccm.
 3. The method of claim 1 wherein the firstflow rate is between about 50 sccm and about 250 sccm.
 4. The method ofclaim 1 wherein the second flow rate is at least about 1000 sccm.
 5. Themethod of claim 1 wherein the second flow rate is at least about fourtimes the first flow rate.
 6. The method of claim 1 wherein the thirdenclosure pressure is at least about nine times the second enclosurepressure.
 7. The method of claim 1 wherein the flow rate of the purgegas is increased to the second flow rate promptly upon reaching thesecond enclosure pressure.
 8. The method of claim 1 further comprising,after increasing the pressure within the enclosure to the thirdenclosure pressure, introducing a flow of a second precursor gas to theenclosure with the pressure within the enclosure at a fourth enclosurepressure, a difference between the third enclosure pressure and thefourth enclosure pressure being about 0-10% of the fourth enclosurepressure.
 9. The method of claim 8 wherein the fourth enclosure pressureis approximately equal to the first enclosure pressure.
 10. The methodof claim 8 wherein the third enclosure pressure is approximately equalto the fourth enclosure pressure.
 11. The method of claim 8 furthercomprising, after introducing the flow of the second precursor gas:terminating the flow of the second precursor gas; reducing pressurewithin the enclosure to the second enclosure pressure while introducinga flow of a purge gas into the enclosure at the first flow rate; andincreasing flow rate of the purge gas to the second flow rate andincreasing the pressure within the enclosure to the third enclosurepressure.
 12. The method of claim 8 further comprising, afterintroducing the flow of the second precursor gas: terminating the flowof the second precursor gas; reducing pressure within the enclosure to afifth enclosure pressure while introducing a flow of a purge gas intothe enclosure at the first flow rate, a difference between the fifthenclosure pressure and the first enclosure pressure being at least 90%of the difference between the base pressure and the first enclosurepressure and the fifth enclosure pressure being different from thesecond enclosure pressure; and increasing flow rate of the purge gas tothe second flow rate and increasing the pressure within the enclosure toa sixth enclosure pressure, a difference between the sixth enclosurepressure and the fourth enclosure pressure being about 0-10% of thefourth enclosure pressure.
 13. A method of depositing a material on amicrofeature workpiece, comprising: positioning a plurality ofmicrofeature workpieces within an enclosure of a processing system, eachof the microfeature workpieces having a surface; exposing the surfacesof the microfeature workpieces to a first precursor gas at a firstenclosure pressure to allow at least a monolayer of the first precursorgas to be adsorbed on the surfaces of the microfeature workpieces;reducing pressure within the enclosure to a second, lower enclosurepressure in a pump-down process, the pump-down process comprisingwithdrawing gas from the enclosure while introducing a purge gas at afirst flow rate of no greater than about 250 sccm for a first period oftime, the pump-down process reducing a partial pressure of the firstprecursor gas within the enclosure; and after the pump-down process,purging the enclosure in a purge process, the purge process comprisingintroducing the purge gas at a second flow rate of at least about 1000sccm for a second period of time and allowing the enclosure pressure toincrease to a third enclosure pressure that is greater than the secondenclosure pressure.
 14. The method of claim 13 wherein the first flowrate is at least about 50 sccm.
 15. The method of claim 13 wherein thesecond flow rate is at least about 2000 sccm.
 16. The method of claim 13wherein the third enclosure pressure is at least about nine times thesecond enclosure pressure.
 17. The method of claim 13 wherein the flowrate of the purge gas is increased to the second flow rate promptly uponreaching the second enclosure pressure.
 18. The method of claim 13wherein the processing system has a base pressure at the first flow rateand a difference between the second enclosure pressure and the firstenclosure pressure being at least 90% of the difference between the basepressure and the first enclosure pressure.
 19. The method of claim 13wherein the partial pressure of the first precursor gas within theenclosure decreases at a first rate profile during the pump-down processand the partial pressure of the first precursor gas decreases at asecond rate profile during the purge process, the first rate profilehaving an initial rate and a terminal rate, the initial rate beingsubstantially greater than the second rate and the second rate beinggreater than the terminal rate.
 20. The method of claim 13 wherein thepartial pressure of the first precursor gas within the enclosure isdecreased at least two orders of magnitude during the pump-down process.21. The method of claim 13 further comprising, after the purge process,exposing the surfaces of the microfeature workpieces to a secondprecursor gas at a fourth enclosure pressure, a difference between thethird enclosure pressure and the fourth enclosure pressure being about0-10% of the fourth enclosure pressure.
 22. The method of claim 21wherein the fourth enclosure pressure is approximately equal to thefirst enclosure pressure.
 23. The method of claim 21 wherein the thirdenclosure pressure is approximately equal to the fourth enclosurepressure.
 24. The method of claim 21 further comprising, after exposingthe surfaces of the microfeature workpieces to the second precursor gas,repeating the pump-down process to reduce a partial pressure of thesecond precursor gas within the enclosure, then repeating the purgeprocess.
 25. The method of claim 21 wherein the pump-down process is afirst pump-down process and the purge process is a first purge process,further comprising, after exposing the surfaces of the microfeatureworkpieces to the second precursor gas, carrying out a second pump-downprocess to reduce a partial pressure of the second precursor gas withinthe enclosure then carrying out a second purge process, the secondpump-down process continuing for a third period of time that differsfrom the first period of time.
 26. A method of depositing titaniumnitride on a microfeature workpiece, comprising: positioning a pluralityof microfeature workpieces in a spaced relationship within an enclosureof a processing system, each of the microfeature workpieces having asurface; introducing a flow of a first precursor gas to the enclosure toexpose the surfaces of the microfeature workpieces to the firstprecursor gas at a first enclosure pressure and allowing at least amonolayer of the first precursor gas to be adsorbed on the surfaces ofthe microfeature workpieces, the first precursor gas comprisingtitanium; reducing pressure within the enclosure by withdrawing gas fromthe enclosure with a vacuum while introducing a purge gas at a firstflow rate of no greater than about 250 sccm for a first period of timeto reduce the pressure within the enclosure to a second, lower enclosurepressure and to decrease a partial pressure of the first precursor gaswithin the enclosure, the processing system having a base pressure atthe first flow rate and a difference between the second enclosurepressure and the first enclosure pressure being at least 90% of thedifference between the base pressure and the first enclosure pressure;upon reaching the second enclosure pressure, purging the enclosure bywithdrawing gas from the enclosure with a vacuum while introducing thepurge gas at a second flow rate of at least 1000 sccm for a secondperiod of time and allowing the enclosure pressure to increase to athird enclosure pressure that is greater than the second enclosurepressure and to further decrease the partial pressure of the firstprecursor gas within the enclosure; and after reaching the thirdenclosure pressure, exposing the surfaces of the microfeature workpiecesto a second precursor gas at a fourth enclosure pressure, a differencebetween the third enclosure pressure and the fourth enclosure pressurebeing about 0-10% of the fourth enclosure pressure, the second precursorgas comprising nitrogen.
 27. The method of claim 26 further comprising,after exposing the surfaces of the microfeature workpieces to the secondprecursor gas: reducing pressure within the enclosure by withdrawing gasfrom the enclosure with the vacuum while introducing the purge gas at athird flow rate of no greater than about 250 sccm for a third period oftime to reduce the pressure within the enclosure to a fifth enclosurepressure and to decrease a partial pressure of the second precursor gaswithin the enclosure, the processing system having a second basepressure at the third flow rate and a difference between the fifthenclosure pressure and the fourth enclosure pressure being at least 90%of the difference between the second base pressure and the fourthenclosure pressure; and upon reaching the fifth enclosure pressure,purging the enclosure by withdrawing gas from the enclosure with avacuum while introducing the purge gas at a fourth flow rate of at least1000 sccm for a second period of time and allowing the enclosurepressure to increase to a sixth enclosure pressure that is greater thanthe fifth enclosure pressure and to further decrease the partialpressure of the second precursor gas within the enclosure.
 28. A methodof depositing a material on a plurality of microfeature workpieces heldin a spaced relationship within an enclosure of a processing system, theenclosure including a first precursor gas and having a first enclosurepressure, the method comprising: reducing pressure within the enclosureto a second enclosure pressure that is less than the first enclosurepressure, the processing system having a base pressure and a differencebetween the second enclosure pressure and the first enclosure pressurebeing at least 90% of the difference between the base pressure and thefirst enclosure pressure; after reducing the pressure within theenclosure to the second enclosure pressure, introducing a flow of apurge gas into the enclosure and increasing the pressure within theenclosure to a third enclosure pressure, the third enclosure pressurebeing greater than the second enclosure pressure; and after increasingthe pressure within the enclosure to the third enclosure pressure,introducing a flow of a second precursor gas to the enclosure with thepressure within the enclosure at a fourth enclosure pressure, adifference between the third enclosure pressure and the fourth enclosurepressure being about 0-10% of the fourth enclosure pressure.
 29. Themethod of claim 28 wherein the fourth enclosure pressure isapproximately equal to the first enclosure pressure.
 30. The method ofclaim 28 wherein the third enclosure pressure is approximately equal tothe fourth enclosure pressure.
 31. The method of claim 28 furthercomprising, after introducing the flow of the second precursor gas:terminating the flow of the second precursor gas; then reducing pressurewithin the enclosure to the second enclosure pressure; and thenintroducing a flow of the purge gas and increasing the pressure withinthe enclosure to the third enclosure pressure.
 32. The method of claim28 further comprising, after introducing the flow of the secondprecursor gas: terminating the flow of the second precursor gas;reducing pressure within the enclosure to a fifth enclosure pressurewhile introducing a flow of the purge gas, a difference between thefifth enclosure pressure and the first enclosure pressure being at least90% of the difference between the base pressure and the first enclosurepressure and the fifth enclosure pressure being different from thesecond enclosure pressure; and introducing the purge gas to theenclosure and increasing the pressure within the enclosure to a sixthenclosure pressure, a difference between the sixth enclosure pressureand the fourth enclosure pressure being about 0-10% of the fourthenclosure pressure.
 33. A microfeature workpiece processing systemcomprising: an enclosure adapted to receive a plurality of microfeatureworkpieces for simultaneous treatment; a gas supply adapted toselectively deliver a first gaseous precursor, a second gaseousprecursor, and a purge gas to the enclosure; a vacuum; and aprogrammable controller operatively coupled to the gas supply and thevacuum, the controller being programmed to: introduce a flow of thefirst precursor gas to the enclosure with a pressure within theenclosure at a first enclosure pressure; terminate the flow of the firstprecursor; reduce pressure within the enclosure to a second, lowerenclosure pressure in a pump-down process, the pump-down processcomprising operating the vacuum source to withdraw gas from theenclosure while introducing the purge gas from the gas supply to theenclosure at a first flow rate of no greater than about 250 sccm for afirst period of time; and after the pump-down process, purge theenclosure in a purge process, the purge process comprising introducingthe purge gas from the gas supply to the enclosure at a second flow rateof at least about 1000 sccm for a second period of time and allowing theenclosure pressure to increase to a third enclosure pressure that isgreater than the second enclosure pressure.
 34. The microfeatureworkpiece processing system of claim 33 wherein the first flow rate isat least about 50 sccm.
 35. The microfeature workpiece processing systemof claim 33 wherein the second flow rate is at least about 2000 sccm.36. The microfeature workpiece processing system of claim 33 wherein thethird enclosure pressure is at least about nine times the secondenclosure pressure.
 37. The microfeature workpiece processing system ofclaim 33 wherein the flow rate of the purge gas is increased to thesecond flow rate promptly upon reaching the second enclosure pressure.38. The microfeature workpiece processing system of claim 33 wherein thecontroller is further programmed to, after the purge process, introducea flow of the second precursor gas from the gas supply to the enclosurewith the pressure within the enclosure at a fourth enclosure pressure, adifference between the third enclosure pressure and the fourth enclosurepressure being about 0-10% of the fourth enclosure pressure.
 39. Themicrofeature workpiece processing system of claim 38 wherein the fourthenclosure pressure is approximately equal to the first enclosurepressure.
 40. The microfeature workpiece processing system of claim 38wherein the third enclosure pressure is approximately equal to thefourth enclosure pressure.
 41. The microfeature workpiece processingsystem of claim 38 wherein the controller is further programmed to,after introducing the flow of the second precursor gas: terminate theflow of the second precursor gas; repeating the pump-down process; thenrepeating the purge process.
 42. The microfeature workpiece processingsystem of claim 38 wherein the controller is further programmed to,after introducing the flow of the second precursor gas: terminate theflow of the second precursor gas; reduce pressure within the enclosureto a fifth enclosure pressure while introducing a flow of the purge gasinto the enclosure from the gas supply at a third flow rate, wherein thefifth enclosure pressure differs from the second enclosure pressure orthe third flow rate differs from the first flow rate; and increase flowof the purge gas to a fourth flow rate and increasing the pressurewithin the enclosure to a sixth enclosure pressure, a difference betweenthe sixth enclosure pressure and the fourth enclosure pressure beingabout 0-10% of the fourth enclosure pressure.